A vehicle occupant system for restraining a vehicle occupant at the time of a crash or other high acceleration situations is designed for a wide range of the build of the vehicle occupant, but can provide an optimum performance only when it is designed for a more specific type of vehicle occupant. The vehicle occupant restraint system as used herein may include air bag systems, seat belt pretensioners, anti-submarine systems and active knee bolster systems among others. However, in practice, the stature of the vehicle occupant can vary a great deal, and a certain degree of compromise is unavoidable. This problem can be mitigated by detecting the nature of the vehicle occupant by using a suitable senor and controlling the vehicle occupant restraint system according to the detected nature of the vehicle occupant.
For such an approach to be feasible, the sensor must be capable of identifying the vehicle occupant both reliably and accurately. Japanese patent publication 2001-180353 discloses an arrangement for detecting the magnitude of the load of the vehicle occupant. The contents of this Japanese patent application is hereby incorporated in this application by reference. Japanese patent publication 2001-294119 discloses such a sensor using both a load sensor and a proximate sensor to the end of detecting both the weight and size of the vehicle occupant. However, according to such previous proposals, it was difficult to achieve both the reliability and precision that are required for the contemplated purposes. Also, such sensors interfere with the existing seat design, and this undesirably adds to the cost of the seat. In particular, a vehicle seat is sometimes equipped with a seat beater, and it can seriously impair the performance of the sensor if the sensor is incorporated in the seat cushion or the upholstery member.